El Niño and La Niña
By Joan Whetzel
During the winter months, two weather patterns occur along the Pacific coasts of the Americas, known as El Niño and La Niña. These are a part of the seasonal climate that includes predictable rainfall and temperature patterns. Specific conditions must be present in order for El Niño and La Niña to occur, however.
The Weather that Spawns these Phenomena
At the latitudes that were higher than the equatorial regions, El Niño and La Niña are two of the factors influencing the climate, especially during the winter months. For the continental US, temperatures in the North Central States are warmer than usual during El Niño winters, whereas temperatures run cooler than usual for Southeastern and Southwestern continental US. La Niña patterns create warmer wetter patterns in the North Central States and dry, warm conditions in the southwest and southeast. In South America, the El Niño and La Niña weather patterns are driven by the sea surface temperatures off the coast.
La Niña
La Niña weather patterns are characterized by cooler than normal surface temperatures in the equatorial regions of the Pacific which makes the trade winds stronge. This in turn, stirs up the deeper colder waters from the ocean floor. The cooler water, in turn, cools and dries the air which reduces cloud cover and rainfall amounts. La Niña, translates to "The Little Girl," but is sometimes called a "cold event" or a "cold episode" in South America. La Niña weather patterns reinforce Pacific circulation, which allows a large ridge of high pressure to develop and strengthen the Canadian jet stream, binging storm systems that carry cooler air and precipitation with them.
El Niño
El Niño brings with it warmer than usual temperatures in the winter months, usually around or near Christmas. South American fishermen who first recognized the patterns applied the moniker "El Niño" for the Christ Child. El Niño weather conditions bring warmer than normal surface temperatures in the equatorial regions of the Pacific. These warmer Pacific surface temperatures increase the rainfall in Southern States as well as in Peru, sometimes causing flooding in these regions, while creating drought conditions along the Western Pacific and conditions like brush fires in Australia. El Niño diminishes and reverses direction of the trade winds.
Resources
NOAA. What Is El Niño?
http://www.pmel.noaa.gov/tao/elNiño/el-Niño-story.html
NOAA. What is la Niña?
